PA2 - Pascal 2

Programming paradigms 2
Doc. RNDr. Pavel Satrapa, Ph. D.
Email: pavel.satrapa (at) tul.cz
Tel: +420 48 535 3685
Office: A9

Some useful links for our PAP course: (Satrapa's presentations)

Programming paradigms 1
http://www.kai.vslib.cz/~satrapa/en/programming/

Programming paradigms 2
http://www.kai.vslib.cz/~satrapa/en/paradigms/

Links to Scheme Resources
http://scheme.com/resources.html
http://schemers.org/

The Scheme-Programming Language
R. Kent Dybvig
http://scheme.com/tspl3/

Lesson #1:
Modules (units)



Lesson #2:
Objects (OOP)



Lesson #3:
(SWI-Prolog)

parent(alfons,frank).
parent(alfons,vera).
parent(emily,frank).
parent(emily,vera).

parent(frank,bob).
grandparent(alfons,bob).


parent(ann,nicol).

parent(ann,mark).
parent(mark,jane).
kokot(mark,margoska).

grandparent(X,Y) :- parent(X,Z), parent(Z,Y).

ancestor(X,Y) :- parent(X,Y).
ancestor(X,Y) :- parent(X,Z), ancestor(Z,Y).

Lesson #4:
Download a new program DrScheme and have fun.
Choose the program language - Teaching language - Intermediate Student.
Play a little bit with the basic function in the down part. DrSchem the begining.
How to designe the program.

Next step is to try out the uper part.
Write:
(define(twice x)
(* 2 x))

(twice 5)
(* 2 (+ 4 6))
(+ 1 2 3)
and check out function like Step , Check Syntax, Run, Stop.
If you need some help click on help.
Other examples:
(sqrt (+ (expt 10 2) (expt 15 2)))
or
(< (expt 2 10) (expt 10 2))
or
(max (expt 2 10) (expt 10 2))
or
(list (expt 2 10) (expt 10 2))

Lesson #5:

Examples:

(define (circlearea r)
(* 3.14 (* r r)))
(define (ringarea outer inner)
(- (circlearea outer) (circlearea inner)))
(ringarea 8 2)

... result=188.4

---

(define (quadeq a b c)
(list (root1 a b c)
(root2 a b c)))
(define (root1 a b c)
(/ (+ (- b) (sqrt (discrim a b c))) (* 2 a)))
(define (root2 a b c)
(/ (- (- b) (sqrt (discrim a b c))) (* 2 a)))
(define (discrim a b c)
(- (* b b) (* 4 a c)))
(quadeq 1 1 -12)

... result= (list 3 -4)

---

(define (hypothenuse a b)
(sqrt (+ (* a a) (* b b))))
(hypothenuse 3 4)

... result= 5

---

(define (lsecond L)
(car (cdr L)))
(define (last L)
(car (reverse L)))
(define (lastcdr L)
(reverse (cdr (reverse L))))
(define (skipsecond L)
(cons (car L) (cdr(cdr L))))
;; second option for skipsecond
(define (skipsecond2 L)
(append (list (car L)) (cdr(cdr L))))
 
(define (swap L)
(append (cdr L) (list(car L))))
;; second option for swap
(define (swap2 L)
(cons (car(cdr L)) (list (car L))))
 
(lsecond '(1 2 3 4 5))
(last '(1 2 3 4 5))
(lastcdr '(1 2 3 4 5))
(skipsecond '(1 2 3 4 5))
(skipsecond2 '(1 2 3 4 5))
(swap '(1 2))
(swap2 '(1 2))

Results:
2
5
(list 1 2 3 4)
(list 1 3 4 5)
(list 1 3 4 5)
(list 2 1)
(list 2 1)


Lesson #5:

Examples:

Create boolean function (inbetween a b c) a<=b<=c

(define (inbetween a b c)
(cond
[(and (<= a b) (<= b c)) #t]
[else #f]
))
(inbetween 1 2 3)

or

(define (inbetween a b c)
(and (<= a b) (<= b c) #t))
(inbetween 1 2 3)

... result= true

---

Create numeric function which limits x to the interval from min to max

(define (limiter min x max)
(cond
[(< x min) min]
[(> x max) max]
[else x]))
(limiter 0 19 100)
(limiter 0 -5 100)
(limiter 0 250 100)

Results
19
0
100

---

(define (sumlist L)
(cond
[(empty? L) 0]
[else (+ (car L) (sumlist(cdr L)))]
))
;sumarize the positive list
(define (poslist L)
(cond
[(empty? L) 0]
[(< (car L) 0) (poslist(cdr L))]
[else (+ (car L) (poslist(cdr L)))]
))
(sumlist '(-1 -1))
(poslist '(-1 -1 5))

Results
-2
5

---

HW task!
-create a function (last L) returning the last element of the list L.. DONT USE THE REVERSE FUNCTION

Lesson #6:

Examples:

(define-struct ware (name price amount))
(define depot  (list (make-ware "Coke" 12 100)
                     (make-ware "Pepsi" 11 200)
                     (make-ware "Sprite" 10 300)))
(define (find-price name L)
  (cond
    [(empty? L) 0]
    [(string=? name (ware-name (car L))) (ware-price (car L))]
    [else (find-price name (cdr L))]
    ))
;;Create a function named depot-value which calculates the global value of all wares
;;in the depot
 
(define (depot-value L)
  (cond
    [(empty? L) 0]
    [else (+ (global-price (car L))
             (depot-value (cdr L)))]
    ))
 
(define (global-price W)
  (* (ware-price W) (ware-amount W)))
 
(find-price "Coke" depot)
(depot-value depot)

Results
12
6400

---

HW task!
-create a function

; create function (bill-price order), the order is a list of lists
; (("apple" 2) ("tomato" 1)) - single sublist for every ware, contains the name ans the
; number of pieces purchased

Lesson #7:

Examples:

(define (findsecond Max SecMax L)
  (cond
    [(empty? L) SecMax]
    [(<= Max (car L)) (findsecond (car L) Max (cdr L))]
    [(<= (car L) SecMax) (findsecond Max SecMax (cdr L))]
    [else (findsecond Max (car L) (cdr L))]
    ))
 
(define (max-second L)
  (findsecond (max (car L) (second L))
              (min (car L) (second L))
              (cdr (cdr L))))
(max-second '(15 10 20 17 8))
;;quickest solution for lazy students
(second (quicksort '(15 10 20 17 8) >))

Results
17
17

---

(define (nearest_to_avg L)
  (cond
    [(empty? L) #f]
    [else (nearest (car L)
                   (avg L)
                   (cdr L))]
    ))
 
(define (avg L) (/(sum L) (length L)))
(define (sum L)
  (cond
    [(empty? L) 0]
    [else (+ (car L) (sum(cdr L)))]
    ))
 
(define (nearest Candidate Target L)
  (cond
    [(empty? L) Candidate]
    [(< (abs (- Candidate Target))
        (abs (- (car L) Target))) (nearest Candidate Target (cdr L))]
    [else (nearest (car L) Target (cdr L))]
    ))
 
(nearest_to_avg '(6 10 15 5))

Results
10

---

HW task!

quick sort for the last task...


Demo exam:
1.
Create function (f a b) evaluateing
((a/b) + (b/a)) /(a*b)

2.
Create function (select n L) selecting n/th element
from list L (if n> length (L) return #f)

3.
We have following definition of department:
(define-stuct dept (name employees))
where department name is a string and employees is a list of strings containing names of employees working in the departmet. Create function (isemployee name department) which returns #t if department contains employee with the given name.

Results:

;1 Task
(define (f a b)
(/ (+ (/ a b) (/ a b)) (* a b)))
(f 4 2)
;should be 0.5

;2 Task

(define (select n L)
(cond
[(empty? L) "the number is not in the list"]
[(> n (length L)) ((length L))]
[(<= n 1) n) (car L)]
[else (select (- n 1) (cdr L))]

))

(select 7 '( 2 3 4 5 6 7))

;3 Task
(define-struct dept (name employees))
(define (isempoyee name department)
(searchstring name ( dept-employees department)))
(define (searchstring s L)
(cond
[(emty? L)#f]
[(string=? s (car L)) #t]
[else (searchstring s (cdr))]
))